Dc dc charging

Submitted: Saturday, May 17, 2014 at 20:55
ThreadID: 107821 Views:1837 Replies:9 FollowUps:17
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I have a duel battery system in my ute with one deep cycle battery under the bonnet and the other under the tray in the rear. It has 6b&s cable between. If I was to use a ctek dc to dc charger to charge the auxiliary batteries would the 4m of 6b&s cable between the batteries be an issue? Eg too long? I also have a slide on camper that goes on my ute. It has 2 batteries in there too. Probably 2 m of cable between battery under the tray to batteries in camper. Could all these batteries be charged by a dc dc charger without issue with the different long cable lengths? At the moment there all just charging from the alternator but there not charging to full charge. Just want to know what the options are?
Cheers
Malcolm
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Reply By: HKB Electronics - Saturday, May 17, 2014 at 21:19

Saturday, May 17, 2014 at 21:19
A DCDC charger should be as close as possible to the batteries/s it is charging.

A charger would run fine with that length of cable.

If you use one charger for all those batteries recharge time will be long.

What make is your vehicle, can/do you have a booster diode fitted?

Why do you feel your battery/s aren't being fully charged?

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Leigh

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Follow Up By: Malmac_123 - Saturday, May 17, 2014 at 23:09

Saturday, May 17, 2014 at 23:09
I have a2009 Toyota hilux. I've got a booster diode fitted which should make the alternator put out 14.1v??

When driving for a long time (weeks) with no accessories running from the auxiliary batteries on the battery monitor it says 14.1 when the car runs but it only ever gets to 12.6 max when there not connected to the starter battery.

Also another question can you run a conventional duel battery system with just the isolator and a dc dc charger at the same time to the same aux batteries? Would that damage the dc dc charger?

I'm just trying to find the best way of charging the batteries in the car and camper.
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Follow Up By: The Bantam - Sunday, May 18, 2014 at 00:01

Sunday, May 18, 2014 at 00:01
we keep comming back to how you are assessing that the batteries are or ar not fully charged.

it must be understood that batteries have a different terminal voltage while under charge and while at rest.

the only reliable way to assess state of charge ( unless you can measure the specific gravity of the electrolite) is to measure resting voltage.

The battery needs to be rested for at least a hour ..much longer if real accuracy is required.

Then if you are realy going to claim accuracy you need to temperature correct.

Nominaly anything above 12.5 volts is considered charged.


some of the tables read that 12.7 volts is 100% charge....but there are many batteries that will never hold 12.7 volts.

There are plenty of batteries out there that go their whole life ..by that standard and never get "fully charged".

This whole notion of "fully charged" and the necessity to "fully charge" a battery is confused and over stated in my opinion.

Now you said..

I have a2009 Toyota hilux. I've got a booster diode fitted which should make the alternator put out 14.1v??

So what does it actually put out...measured with an accutrate meter.

I have fitted a new replacement alternator to one of my vehicles and it outputs 14.4 volts.

if you started with 13.8, a booster diode should give you 14.4.

cheers
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Follow Up By: HKB Electronics - Sunday, May 18, 2014 at 09:40

Sunday, May 18, 2014 at 09:40
Mal_mac123

Depending on the type of battery fitted, 12.6V could well be fully charged!

From what you have written sounds like your setup is working as intend, I would leave as is and see how it performs on your trip.

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Leigh

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Follow Up By: HKB Electronics - Sunday, May 18, 2014 at 09:43

Sunday, May 18, 2014 at 09:43
PS

Forgot to add, as Bantam has written, asking an alternator to charge 5 batteries is a big ask.

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Follow Up By: Malmac_123 - Sunday, May 18, 2014 at 11:04

Sunday, May 18, 2014 at 11:04
The only reason I was thinking they wernt charged was because when my camper batteries are charged with 240 charger and it says their charged. The volt metre reads over 13.1v
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Follow Up By: Allan B (Member, SunCoast) - Sunday, May 18, 2014 at 11:36

Sunday, May 18, 2014 at 11:36
As Bantam has said you must wait for 1 hour after the charger has been removed before obtaining a meaningful voltage reading from the battery.

Whilst charging, the battery voltage will read over 14.0 volts, maybe as much as 14.5v.
After full charging, it will drop to about 13.0 volts immediately after the charger is disconnected then fall slowly over an hour or so to about 12.5 volts as the "surface charge" decays. It will settle quicker if a discharge load is on the battery, but this should be avoided as then a conclusion cannot be reached in regard to the initial state of charge. This 12.5 volts is the true State of Charge of the battery.
All readings should be taken directly on the battery terminals.
The "Charge Complete" indicator of your 240v charger takes this "surface charge" into account.

The above voltage references are nominal and will vary slightly with individual batteries and with the accuracy of your voltmeter. Some installed panel meters can be in error by as much as 1 volt.
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Allan

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Reply By: The Bantam - Saturday, May 17, 2014 at 21:42

Saturday, May 17, 2014 at 21:42
As has been mentioned..what is your charging voltage?

NOW another thing to consider......4 batteries in the vehicle....that is a big ask for an alternator.

ANOther thing to remember....charging batteries takes time....this is unavoidable...it may take 6- 8 or more hours to bring a battery to full charge from a low state of charge regardless of the capacity or type of the charger.

If you are camping over night or for a couple of days and then driving a couple of hours......nothing will get your batteries up to full charge in that time.

cheers

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Follow Up By: Malmac_123 - Saturday, May 17, 2014 at 23:16

Saturday, May 17, 2014 at 23:16
I have a diode booster for the alternator which I think puts it up to 14.1v

We're going traveling next year for 3 months and I'm getting my car and camper sorted.
There is a 240 charger in the camper that can fully charge the batteries if we stay at a caravan park but for at least a week or 2 I'll be doing the gibb river rd probably with no power.

I just want to find out the best way to charge the batteries weather through an isolator. Dc dc charger, or solar or a combination.

Just want to get some advice on what will work
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Reply By: Malmac_123 - Saturday, May 17, 2014 at 23:21

Saturday, May 17, 2014 at 23:21
Does dc dc charging (40amp charger) charge the batteries quicker than through an isolator ?
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Follow Up By: Allan B (Member, SunCoast) - Saturday, May 17, 2014 at 23:36

Saturday, May 17, 2014 at 23:36
Not necessarily but in certain circumstances it may, especially if you are using a 40 Amp dc-dc charger.

But bear in mind that a 40 amp charger will not always pump 40A into your battery, that rating is the maximum charger output which it will deliver if called upon. The actual current will be a function of a number of conditions especially the state of charge of the battery.

The intended purpose of a dc-dc charger is to overcome a low input voltage, usually caused by voltage drop in the cables. For this reason it needs to be installed close to the battery that it is charging.
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Allan

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Reply By: Allan B (Member, SunCoast) - Saturday, May 17, 2014 at 23:26

Saturday, May 17, 2014 at 23:26
Mal,

Apart from the direct answers you get from others, you may find this blog showing sample wiring diagrams useful.

Cheers
Allan

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Reply By: Travelling - Sunday, May 18, 2014 at 10:09

Sunday, May 18, 2014 at 10:09
The only way to do the job properly and get fully charged batteries is to use another Ctek D250S Dual. Well worth the money when you consider the cost of batteries. Ensuring batteries are fully charged correctly increases battery life dramatically.
Alternator voltage boosting devices are rubbish for charging deep cycle batteries. Alternators are crude battery charging devices and the alternator can only sense the first battery in the circuit. The only charge that flows to the other batteries is the potential voltage difference between the main and auxiliary battery. Calcium vehicle starting batteries handle the crude charging from a vehicle alternator well, unlike proper deep cycle batteries.
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Follow Up By: The Bantam - Sunday, May 18, 2014 at 12:08

Sunday, May 18, 2014 at 12:08
here we go with the old " cant charge properly off an alternator" chestnut.

calling an alternator crude is not accurate or fair.

Unless the alternator is one of a few types it does not do any sensing of the battery..it outputs a fixed regulated voltage.

We have been charging lead acid batteries with constant voltage chargers for many decades with good results and it remains THE most reliable way to charge a lead acid battery of any type.

as far as multi stage chargers...yeh under certain circumstances they will stick more chage to a battery faster than a similar capacity fixed voltage charger....BUT....they are less clever than most people want to believe and they certainly do not work as well when connected to other than a single battery or a group of matched batteries.

AND a multi stage charge has no advantage whatsoever if it is way lower in capacity than a fixed voltage charger and it spends all its life in one mode of its many, because it is too small for the battery capacity.




the argument that "fully charging" batteries increases their life..is well...contravercial...at the lest over simplistic.

we can start with the argument about what IS "fully charged"

The only thing that is realy certain is that lead acid batteries resent being chronicaly undercharged.....possibly one of the biggest causes of battery failure and camper disapointment is failing to return enough charge to cover the load drawn pluss losses on a daily basis.
Thus the battery decends into a lower and lower state of charge every day till it fails.

AND as I have said before...generalisations about batteries are quite unreliable, because, these days the manufacturers can mainpulate so many factors about batteries.

As far as calcium...just about every reputable modern battery will have some calcium in the plates, because it improves just about every factor of lead acid battery performance........

As for "proper deep cycle battery"..what would that be exactly....there are many deep cycle batteries...some wiil tolerate very high charge rates and others will have very poor maximum initial charge rates.

The proper deep cycle batteries in my litlle electric truck will tolerate the current being hammered into them...if you want to call somethig a "proper" deep cycle battery a trojan wett cell certainly is it.

I believe the OPs problems are two fold...firtsly he has insufficient charging capacity for the batteries carried.

and

He is confused or misinformed about what actually constitutes fully charged for his batteries.


cheers
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Follow Up By: HKB Electronics - Sunday, May 18, 2014 at 18:21

Sunday, May 18, 2014 at 18:21
Travelling, I would suggest you do some research, a standard alternator chargers at around 14.4V@24C, a high compensation alternator charges at around 14.1V - 14.4V with booster diode fitted. A CTEK charges at 14.4V a Redarc at.14.5V They are all more or less the same, if the alternator can't charge it then neither can a DCDC charger.

The following statement is totally incorrect:

"The only charge that flows to the other batteries is the potential voltage difference between the main and auxiliary battery. Calcium vehicle starting batteries handle the crude charging from a vehicle alternator well, unlike proper deep cycle batteries."

An alternator float charges, within seconds of the engine starting it will force the cranking battery terminal voltage to 14.4V for example, the isolator will kick in shortly after the car starts and switch the alternators output voltage of 14.4V through to the auxilllary battery also.

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Follow Up By: Travelling - Sunday, May 18, 2014 at 19:10

Sunday, May 18, 2014 at 19:10
Reason why it is a waste of time posting correct information here from technically qualified and experienced qualified engineers in the DC vehicle field.
Waste of time arguing with the wanna be unqualified knowitalls.
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Follow Up By: HKB Electronics - Sunday, May 18, 2014 at 19:40

Sunday, May 18, 2014 at 19:40
Yes I agree completely!

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Follow Up By: The Bantam - Sunday, May 18, 2014 at 23:15

Sunday, May 18, 2014 at 23:15
Traveling....Yeh typical response I'd expect from an engineer..I'm right and won't discuss the matter...then try to belittle the bloke who disagrees or chalenges you.

BTW you have not an inkling of what I am qualified to do or my experience.

How about you address the discussion...perhaps some of the points are not clearly expressed.

cheers

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Reply By: Member - John and Val - Sunday, May 18, 2014 at 10:26

Sunday, May 18, 2014 at 10:26
Malcolm,

I'd suggest connecting the two on-board batteries together and charging them directly from the isolator. Not perfect, but if you are using 6 B&S cable for the 4 metre run should be OK. I'd recommend not relying on chassis return, but providing a decent cable return for the negative side too.

For the camper, I'd run a two core cable from the isolator to the camper batteries. (NOT from the under tray battery, since it is drawing current and hence already reducing the available voltage ). With heavy cables (both positive and negative) to the camper you might get away without a dc-dc charger. If this arrangement can't deliver at least close to 14V at the camper batteries when they are charging at a reasonable rate I'd add a dc-dc charger close to the batteries.

An important consideration that's easily overlooked - you are trying to charge 4 auxilliary batteries plus the cranking battery using an alternator rated at how many amps? The alternator is not rated to deliver high current for hours at a time and is not immortal! Check on its capacity before asking too much of it.

Suggest if you don't already have one that a meter capable of measuring volts and amps would be a very good investment.

Cheers

John
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Reply By: Malmac_123 - Sunday, May 18, 2014 at 11:01

Sunday, May 18, 2014 at 11:01
From what I can understand having the alternator charge 4 batteries is a big ask. If I connect a decent watt solar panel to the batteries would that help to charge the batteries quicker?? Or would the dc dc charger choose either the alternator or solar depending which was giving the most current. I've never had solar panels before, but if I had the setup with just the battery isolator from the starter and a solar panel though a regulator. Would they both provide charge at the same time to achieve the charge required because of how many batteries are in the setup?

Also in people's opinion is 4 batteries over kill?
I have a 40 fridge in the car running.

In the camper I have an 80l fridge
Led lighting used at night for cooking and general seeing at night.
They'll also be used for charging phones and camera batteries
Don't really use high power 12v appliances or inverter

The only section on my trip I'm concerned us the gibb river rd where there is no 240v for about 2 weeks.
Also if I take the camper off for a few days I'll need it to run the fridge and lights.
AnswerID: 532685

Follow Up By: The Bantam - Sunday, May 18, 2014 at 12:19

Sunday, May 18, 2014 at 12:19
there is no such thing as too much battery capacity....agh agh agh more power

By far most people are under provided with battery capacity.

BUT the telling question is how you charge all that lovely capacity.

I think you realy do need to look for some source of sumpimentary charging capacity.

This IS where one of the multi input DC to DC charger systems will be a prodigeous advantage.

They can manage multiple charge inputs and make the best of them......that is their biggest advantage

I think you are looking at some solar pannels and at least a multi input charger for the camper.


don't worry about the Dc to Dc bit or the multistage bit...it is the multi input managment that is going to make on of these things a winner for you.

cheers

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Follow Up By: Echucan Bob - Sunday, May 18, 2014 at 16:19

Sunday, May 18, 2014 at 16:19
Bantam

I agree its nice to have unlimited reserves of power, but if you are using lead acid batteries there is a significant weight penalty. A nice big LiFePO4 battery would be the go, but then there is a significant $ penalty.

I would think a reserve battery for each of his fridges would give him more than enough reserves of power. The fourth battery is just overkill.

Bob

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Follow Up By: The Bantam - Sunday, May 18, 2014 at 23:16

Sunday, May 18, 2014 at 23:16
Um...yeh he alaready has the batteries installed and it unlikly he will be coughing up for lithium any time soon.

cheers
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Reply By: Twinkles - Sunday, May 18, 2014 at 12:17

Sunday, May 18, 2014 at 12:17
I have a Hilux with slide on camper. Under the bonnet is a starter battery and second deep cycle battery of 97Ah. There is an isolator between these. From the second battery I run 10mm cable to the camper. In there is a CTEK 250S and battery 3, also 97Ah. Because I want the under bonnet second battery available for my lighting and fridge, if camper still on car, I have 2 relays with a switch to isolate the CTEK from the line. The CTEK has an isolator as well so can't access battery 2 with it in line. This also serves to enable me to charge battery 2 & 3 with AC charger, also CTEK. There is also a cable from the CTEK for solar, which will charge battery 2 & 3, when I get some panels. Seems to work well.
AnswerID: 532687

Follow Up By: Malmac_123 - Sunday, May 18, 2014 at 12:26

Sunday, May 18, 2014 at 12:26
Could I get you to draw a rough diagram of that setup to have a look at to understand better
Cheers
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Reply By: Twinkles - Sunday, May 18, 2014 at 15:21

Sunday, May 18, 2014 at 15:21
I don't know how to insert an image from computer. It asks for an internet address, URL
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